A user accidentally held down the Ctrl key when trying to type an underscore in a point name, leading to the discovery of this bug.
Steps to reproduce:
Create a new template.
Add a new component (any kind).
Rename a point. In the name field, type Ctrl+Shift+- (i.e. Ctrl-_, or 0x1F, or the Unit Separator character). Nothing shows up in the field in the Edit Point dialog, but a filled downward-pointing triangle will show up in the point label in the graphical template editor.
Now when you try to build a corridor/open corridor objects, and it reads the ITL file, you'll get an XML validation error complaining about the illegal character.